A capacitor may be used to store predetermined data in a memory device such as a dynamic random access memory (DRAM). The capacitor includes capacitor electrodes, referred to as storage and plate nodes, and a dielectric layer interposed between the capacitor electrodes.
Recently, as semiconductor memory devices have become more highly integrated, chip area for a memory cell in semiconductor memory devices has been reduced, and the operating voltage of semiconductor memory devices has been lowered. In this regard, a capacitor, which is one of components of the semiconductor memory device, must have the charge quantity necessary for the operation of the semiconductor memory device even if the projected area of the capacitor is reduced. If the charge quantity is insufficient, many problems such as soft errors and short refresh times of the semiconductor memory device may occur. As can be understood from an equation, Q=CV, the charge quantity is determined as a function of an operating voltage (V) applied to the capacitor and capacitance (C) of the capacitor. However, since the operating voltage (V) is decreased as the memory device becomes more highly integrated, the capacitance (C) must be increased in order to obtain sufficient charge quantity. Accordingly, sufficient capacitance (C) must be ensured even in a smaller area. The capacitance (C) can be represented as the following equation.C=∈S/d  [Equation 1]
In Equation 1, C, ∈, S, and d represent capacitance, the permittivity of a dielectric substance, a sectional area of a pole plate, and a distance between two pole plates, respectively. According to Equation 1, the capacitance is proportional to the permittivity of the dielectric substance and an effective area of a capacitor, and inversely proportional to the thickness of the dielectric substance. In other words, the capacitance is proportional to the surface area of an electrode and the permittivity of the dielectric substance, and inversely proportional to the distance between electrodes. Accordingly, to obtain a capacitor having high capacitance, the surface area of the electrode must be enlarged, or the dielectric layer must have high permittivity. In addition, the distance between the electrodes must be reduced, that is, the thickness of the dielectric substance must be minimized.
Regarding an electrode material of the capacitor, since various characteristics are required due to high integration and high performance of semiconductor devices, a capacitor having a metal-insulator-metal (MIM) structure of a metallic electrode has been employed.